Disposable diapers with fastening tapes becoming elastic during use

ABSTRACT

A disposable diaper includes a liquid permeable topsheet, a liquid impermeable backsheet, and an absorbent member interposed between the topsheet and backsheet. When worn, the diaper forms a front waist body portion, a rear waist body portion, and a crotch portion. The rear waist body portion has at each side, a fastening tape which is designed to reveal elasticity on being pulled in the longitudinal direction of the fastening tape.

TECHNICAL FIELD

This invention relates to a disposable diaper and more particularly to adisposable diaper having a novel fastening tape efficient inproductivity.

BACKGROUND ART

Disposable diapers often have a means for gathering up at the waist toimprove a fit of the waist opening portion while worn, such as fasteningtapes made of an elastic member (see Japanese Patent Publication No.7-61351 and Japanese Utility Model Publication No. 4-10817) or anelastic member that is provided at the rear waist portion.

In order to gather at the waist by the above-mentioned conventionalmeans, an elastic member having elasticity must be fixed at a prescribedposition of a diaper with a necessary step of stretching the elasticmember in a series of a production system. Therefore the elastic membercannot be transported, fixed, and assembled into a diaper in the samemanner as other members, which has caused poor productivity. Further, acomplicated processing step is involved which increases cost.

Japanese Patent Laid-Open No. 7-231913 discloses a porous sheet in whichareas having no elasticity but moisture permeability alternate withareas having no moisture permeability but elasticity. The publicationfurther discloses the use of the porous sheet in absorbent articles, forexample, as a back sheet of a disposable diaper. However, thepublication neither discloses nor suggests use of the porous sheet as afastening tape for diapers.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a disposable diaperthat can be gathered at the waist without reducing productivity orinvolving a complicated processing step.

As a result of extensive study, it has been found that the above objectis accomplished by designing a fastening tape so as to reveal elasticityon pulling to its longitudinal direction.

The present invention has been completed based on this finding. Theinvention provides a disposable diaper which comprises a liquidpermeable topsheet, a liquid impermeable back sheet, and an absorbentmember interposed between the topsheet and the back sheet, and has astructure to form, when worn, a front waist body portion, a rear waistbody portion and a crotch portion, the rear waist body portion having ateach side thereof a fastening tape for fastening the diaper, wherein thefastening tape is designed to reveal elasticity on being pulled in thelongitudinal direction thereof.

The invention provides the above-described disposable diaper, whereinthe fastening tape has a tip portion having a first fastening meansprovided on one surface side thereof, a central portion which revealselasticity on being pulled in the longitudinal direction of the tape,and a fixed portion which is fixed at the rear waist body portion, andthe back sheet is provided with a second fastening means on the surfaceside thereof so that the diaper may be removably fastened by binding thefirst fastening means and the second fastening means.

The invention provides the above-described disposable diaper, whereineither one of the first fastening means and the second fastening meansis made of a male member of a mechanical fastener and the other is madeof a female member of the mechanical fastener or nonwoven fabricengageable with the male member.

The invention provides the above-described disposable diaper, whereinthe central portion of the fastening tape has (a) a plastic deformablearea and (b) a stretchable area, each being formed on at least onesurface side of said central portion and extending in the longitudinaldirection of the tape.

The invention provides the above-described disposable diaper, whereinthe stretchable area (b) is provided on the plastic deformable area (a)in a line, a band or a spiral form.

The invention provides the above-described disposable diaper, wherein aplurality of the stretchable areas (b) alternate with the plasticdeformable areas (a) in the width direction of the tape.

The invention provides the above-described disposable diaper, whereinthe plastic deformable area (a) and the stretchable area (b) have anarea ratio, (a)/(b), of 2/8 to 8/2.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plane view of an example of the disposable diaper of theinvention in its unfolded condition.

FIG. 2 is a perspective view of the disposable diaper of FIG. 1 in itsshaped condition.

BEST MODE FOR CARRYING OUT THE INVENTION

The disposable diaper of the invention is explained with reference toone embodiment by referring to the accompanying drawings. FIG. 1 is aplane view of one embodiment of the disposable diaper of the inventionin its unshaped condition. FIG. 2 is a perspective view of thedisposable diaper of FIG. 1 in its shaped condition.

As shown in FIGS. 1 and 2 the disposable diaper 1 according to thisembodiment comprises a liquid permeable topsheet 2, a liquid impermeableback sheet 3, and an absorbent member 4 interposed therebetween. Thedisposable diaper has a structure comprising portions A, B and C toform, when worn, a front waist portion, a rear waist portion and acrotch portion. The portion B corresponding to the rear waist portionhas a fastening tape 10 at both side edges thereof B1 and B2. Such astructure is the same as in conventionally known disposable diapers.

The topsheet 2, back sheet 3, and absorbent member 4 each has arectangular shape to form the disposable diaper 1 in a rectangular shapeas well.

The topsheet 2, back sheet 3 and absorbent member 4 can be made of anymaterial conventionally employed in disposable diapers with noparticular limitation. When a mechanical fastener (also called a planarfastener or a hook-loop tape) is used as a first fastening means ashereinafter described, the back sheet 3 can be made of hydrophobicnonwoven fabric. It should be understood, however, that the firstfastening means is not limited to the mechanical fastener.

In the disposable diaper 1, the fastening tape 10 is designed to revealelasticity upon being pulled in the longitudinal direction thereof.

The language "designed to reveal elasticity upon being pulled in thelongitudinal direction thereof" as used herein is intended to mean thatthe fastening tape has the structure which shows no elasticity beforeuse but reveals elasticity when stretched by pulling in the longitudinaldirection on use. More specifically, the fastening tape is formed of,for example, a striped sheet or the like hereinafter described.

As shown in FIG. 1, the fastening tape 10 has on one surface sidethereof (the surface side contacting with backsheet) a tip portion 11 onwhich a male member (hooks) of "Magic Tape" (a registered trade name ofa mechanical fastener) is attached as a first fastening means 11a, acentral portion 12 which reveals elasticity on being pulled in itslongitudinal direction, and a fixed portion 13 at which the tape isfixed to the rear waist portion B of the diaper. The back sheet 3 ismade of hydrophobic nonwoven fabric, and the nonwoven fabric itselfserves as a second fastening means. The diaper is removably fitted to awearer by binding the first fastening means 11a and the second fasteningmeans, i.e., the nonwoven fabric forming the back sheet 3.

In the disposable diaper 1 according to this embodiment, the firstfastening means is formed of a male member of a mechanical fastener, andthe second fastening means is formed of nonwoven fabric engageable withthe male member.

As shown in FIG. 1, the fastening tape 10 is formed so as to give (a) aplastic deformable area and (b) a stretchable area on at least one sideof the central portion 12, each extending in the longitudinal directionof the tape substantially in parallel with each other. There may be asingle or a plurality of the stretchable areas (b). In the latter case,the plastic deformable areas (a) and the stretchable areas (b) alternatewith each other in the tape width direction to form stripes. For causingstable elastic property of the fastening tape, the number of thestretchable areas (b) is preferably 1 to 10. Because the tip portion 11has a male member of a mechanical fastener attached to one surface sidethereof, and the fixed portion 13 is fixed to the back sheet 3 via anadhesive, these portions are designed not to reveal elasticity. In otherwords, only the central portion is designed to reveal elasticity.

The fastening tape 10 of the present invention can be formed of a sheethaving on at least one side thereof the above-mentioned plasticdeformable area (a) and stretchable area (b). Such a sheet includes asheet made up of a material forming the plastic deformable area (a)having provided thereon a material forming the stretchable area (b) inthe form of a line, a spiral, etc.

The area ratio of the plastic deformable area (a) to the stretchablearea (b), (a):(b), is preferably 2:8 to 8:2, more preferably 4:6 to 6:4.The weight ratio of the material forming the plastic deformable area (a)to the material forming the stretchable area (b), (a):(b), is preferably2:8 to 8:2.

Where the stretchable area is formed in a line, the line width ispreferably 1 to 10 mm.

The width of the fastening tape 10 is arbitrary according to the size ofthe diaper and is preferably 15 to 50 mm.

Materials forming the plastic deformable area (a) and the stretchablearea (b) are explained below.

The material forming the plastic deformable area (a) is not restricted,when said material has the plastic deformable property. As saidmaterial, polyolefin resins such as polyethylene resin, polypropyleneresin, ethylene propylene copolymer, and the like can be included. Thepreferable polyolefin resins are high-density polyethylene, low-densitypolyethylene, and linear low-density polyethylene (LLDPE). LLDPE havinga density of 0.910 to 0.940 g/cm³ and a melt flow rate (MFR) of 0.1 to 5g/10 min are particularly preferred. The plastic deformable materialcapable of forming a moisture permeable sheet, which is disclosed inJapanese Patent Laid-Open No. 7-231913, can be preferably used. Forexample, the following compositions (1) to (3) are preferably used.

Composition (1): A composition comprising 100 parts by weight of apolyolefin resin, 50 to 400 parts by weight of a filler, and 0.1 to 20parts by weight of a softener.

Composition (2): A composition obtained by melt-kneading 65 to 90 partsby weight of a crystalline polyolefin and 10 to 35 parts by weight of acompound which has miscibility with and solubility in the crystallinepolyolefin at temperatures at and above the melting point of thecrystalline polyolefin but undergoes phase separation from thecrystalline polyolefin at temperatures below the melting point of thecrystalline polyolefin.

Composition (3): A composition obtained by melt-kneading 100 parts byweight of a polyolefin resin and 10 to 100 parts by weight of athermoplastic resin which is incompatible with the polyolefin resin.

The stretchable area (b) constituting the fastening tape of theinvention is an area for imparting elasticity to the fastening tape. Thestretchable area (b), when stretched, preferably has such elasticitythat the residual strain after 50% stretch and relief of the tension isnot more than 20%.

The material forming the stretchable area (b) preferably includesthermoplastic elastomers. Examples of suitable thermoplastic elastomersare styrene elastomers, olefin elastomers, polybutadiene elastomers,polyester elastomers, polyamide elastomers, urethane elastomers, vinylchloride elastomers, fluorine-containing elastomers, ionomer resins,silicone resins, and mixtures thereof. Styrene elastomers and olefinelastomers are particularly preferred.

In order to prevent the stretchable area (b) from temporarily shrinkingafter being stretched together with the plastic deformable area (a), acomposition comprising the thermoplastic elastomer and a polyolefinresin as an additional thermoplastic resin is preferably used as amaterial for forming the stretchable area (b). In this case, styreneelastomers or olefin elastomers are preferably used for theircompatibility with the polyolefin resin.

The polyolefin resin to be combined with the thermoplastic elastomer canbe selected from the same polyolefin resins as used as a material forforming the plastic deformable area (a).

A preferred weight ratio of the styrene elastomer or olefin elastomer tothe polyolefin resin is 80/20 to 20/80, particularly 70/30 to 30/70.

The styrene elastomer includes "Kraton" and "Califlex" both produced byShell Chemical Co., Ltd., and "TUFPRENE" and "SOLPRENE" both produced byAsahi Chemical Industry Co., Ltd. The olefin elastomer includes"Milastomer" produced by Mitsui Petrochemical Industries, Ltd. and"Sumitomo TPE" produced by Sumitomo Chemical Co., Ltd.

When a styrene elastomer composition is used as a material for formingthe stretchable area (b), the most preferred composition comprises (i)0.3 to 0.7 part by weight of a styrene elastomer which is an aromaticvinyl compound-conjugated diene block copolymer having the aromaticvinyl compound content of 10 to 40% by weight with the conjugated dienemoiety thereof being hydrogenated, (ii) 0.2 to 0.6 part by weight of apolyolefin resin, and (iii) 0.05 to 0.3 part by weight of a resin havinga melting point or a softening point of not lower than 80° C. and anaverage molecular weight of 400 to 2000.

The component (i) is a thermoplastic elastomer of aromatic hydrocarbonpolymer type which comprises at least one polymer block of an aromaticvinyl compound and at least one hydrogenated conjugated diene polymerblock.

While the method for obtaining the derivative in which the diene moietyis hydrogenated is not limited, it is preferable for impartingelasticity to the stretchable area (b) that at least 80% of theconjugated diene block(s) be hydrogenated.

The aromatic vinyl compound is a styrene type monovinyl-substitutedaromatic hydrocarbon, preferably styrene. α-methylstyrene, etc. are alsouseful.

The conjugated diene is preferably butadiene, isoprene or a mixturethereof.

The weight ratio of the aromatic vinyl compound polymer block A to theconjugated diene polymer block B is preferably 10/90 to 40/60. The totalnumber average molecular weight of the polymer block A and the polymerblock B is preferably more than 20000, still preferably 30000 to 250000,particularly preferably 40000 to 200000, as measured by gel-permeationchromatography (GPC).

The olefin resin as component (ii) includes olefin thermoplastic resinscomprising homo- or copolymers of α-olefins, such as ethylene,propylene, butylene, etc. Resins generally used in thermoplastic moldingare used. Preferred of them are specific polyethylene or polypropyleneused for the injection or extrusion molding. For use in which softnessis required as in diapers, low-density polyethylene is suitable. Linearlow-density polyethylene (LLDPE) is particularly suitable.

The resin as component (iii) is preferably a resin having a meltingpoint or softening point of not lower than 80° C., still preferably notlower than 100° C., and a number average molecular weight of 400 to2000, preferably 600 to 1500. Such a resin includes hydrogenated terpeneresins and alicyclic hydrogenated resins.

Typical examples of such a resin include "CLEARON" produced by YasuharaYushi K. K. and "ARKON" produced by Arakawa Kagaku Kogyo K. K.

The sheet for forming the fastening tape can easily be obtained byextruding the material for forming the plastic deformable area (a) toobtain a moisture permeable sheet, and extrusion laminating the materialfor forming the stretchable area (b) onto the moisture permeable sheetin places, e.g., in the form of line(s), band(s) or spiral(s).

The disposable diaper 1 according to this embodiment can be put on awearer by stretching the fastening tape 10 by pulling to itslongitudinal direction (the direction indicated by the arrow in FIG. 1)and applying the mechanical fastener 11 (the first fastening means) tothe back sheet 3 to fasten the diaper as shown in FIG. 2.

Because the disposable diaper of the invention has the above-mentionedfastening tape 10, there is no need in the production of the disposablediaper to attach an elastic member, under stretched condition, to aprescribed position of a diaper, thus providing excellent productivity.The fastening tape 10 has no elasticity before use but, when it is puton a wearer (e.g.,baby), it reveals elasticity upon user's (e.g.,mother's) pulling the tape to stretch the plastic deformable area (a).As illustrated in FIG. 2, the fastening tape 10 revealing elasticityforms gathers 20 at the waist so that the waist portion has an improvedfit through the elasticity of the waist gathers 20.

The disposable diaper of the invention is by no means limited to theabove-described embodiment. For example, the sheet for forming thefastening tape may be a striped sheet obtained by co-extrusion of thematerial for forming the plastic deformable area (a) and the materialfor forming the stretchable area (b) in such a manner that plasticdeformable areas (a) and stretchable areas (b) alternative with eachother.

Further, the mechanical fastener as the first fastening means may bereplaced with an adhesive. In this case, the material for forming theback sheet is not limited to nonwoven fabric. While any material ingeneral use may be employable as a back sheet-forming material, it ispreferred in this case to use a sheet material to which the adhesivetape can be removably stuck, or to provide a generally known landingtape on the surface of the back sheet. In these cases, the sheet itselfto which an adhesive tape can be removably stuck or the landing tapeserves as the second fastening means.

On the other hand, a certain shape of female member of the mechanicalfastener or nonwoven fabric may be attached at a prescribed position ofthe surface of the back sheet to provide a second fastening means.

Furthermore, a female member of the mechanical fastener or nonwovenfabric may be attached to the tip portion of the fastening tape toprovide a first fastening means, while a male member may be attached tothe back sheet as a second fastening means.

The fastening tape can be designed to reveal elasticity over the entirearea thereof, and a fastening means may be provided at portions otherthan the tip portion.

Unlike the embodiment shown in FIGS. 1 and 2, a tip portion, a centralportion, and a fixed portion of the fastening tape may be preparedseparately and joined together at the respective ends to form afastening tape as a whole.

The shape of the disposable diaper is not limited to a rectangle asparticularly referred to above. For example, the diaper may have theportion corresponding to the crotch portion in use narrowed to have asandglass-like shape. An elastic member may be provided at the portionscorresponding to the leg opening portions.

The central portion of the fastening tape does not need to havestretchability over the entire area thereof as long as at least part ofit is stretchable to reveal elasticity.

INDUSTRIAL APPLICABILITY

The disposable diaper of the invention is designed to reveal elasticityat the fastening tape thereof through put-on operations of a userwithout being accompanied by reduction in productivity or involvement ofcomplicated processing steps. By virtue of the thus revealed elasticity,the gathers can be formed at the waist portion of the diaper where nogathers had existed before use.

We claim:
 1. A disposable diaper comprising:a liquid permeable topsheet;a liquid impermeable backsheet; an absorbent member interposed betweensaid topsheet and said backsheet; said topsheet, said backsheet, andsaid absorbent member forming a front waist body portion, a rear waistbody portion and a crotch portion when said diaper is worn; and a tapefastener connecting the front waist body portion to said rear waist bodyportion, said tape fastener including a tip portion with a firstfastening means provided on one surface side thereof, said tape fastenerincluding a central portion and a fixed portion, said central portionbeing designed to reveal elasticity when pulled in a longitudinaldirection thereof, said fixed portion being secured to said waist bodyportion, said back sheet being provided with a second fastening means,said first fastening means being removably connected to said secondfastening means, said central portion of said tape fastener furtherincluding a plastic deformable area and a stretchable area forming asingle planar sheet and extending in a longitudinal direction of saidtape fastener, said plastic deformable area and said stretchable areabeing separated from each other in a tape width direction, said plasticdeformable area forming gathers when said diaper is worn where saidfirst fastening means is removably connected to said second fasteningmeans, whereby said tape fastener substantially improves a fit of saidfront and said rear waist body portions on a user while substantiallyincreasing manufacturing efficiency of said diaper.
 2. The disposablediaper according to claim 1 wherein either one of said first fasteningmeans and said second fastening means is made of a male member of amechanical fastener and the other is made of a female member of themechanical fastener or nonwoven fabric engageable with said male member.3. The disposable diaper according to claim 1 wherein said stretchablearea is provided in a line, a band or a spiral form.
 4. The disposablediaper according to claim 1 wherein a plurality of stretchable areasalternate with a plurality of plastic deformable areas in the widthdirection of the fastening tape.
 5. The disposable diaper according toclaim 1 wherein said plastic deformable area and said stretchable areahave an area ratio of 2/8 to 8/2.
 6. The disposable diaper according toclaim 1 wherein the plastic deformable area comprises polyolefin resin.7. The disposable diaper according to claim 1 wherein the stretchablearea comprises styrene elastomer or olefin elastomer.
 8. The disposablediaper according to claim 7, wherein the stretchable area furthercomprises polyolefin resin.